Over the last 50 years, contraception has had a major impact on human society and influenced the worldwide distribution of family sizes and the variability of fertility rates (Bongaarts and Watkins, 1996; Bongaarts, 1997). This impact can be largely attributed to female contraceptive methods, their availability and economic and social costs.
Male contraception, on the other hand, has had much less of a global impact, being largely limited to condoms and vasectomy (Nass and Strauss, 2004). Female hormonal contraceptives work through the mechanism of anovulation and the goal of male hormonal contraceptive research is analogous, namely the suppression of spermatogenesis to produce azoospermia. However, achievement of this goal in a reliable way for a diverse population of men is still many years away (Grimes et al., 2005; Potts, 1996).
Even further away is the dream of a non-hormonal male contraceptive in which it may be envisioned that spermatozoa do not develop, or do not swim, or do not fertilize or some combination of these spermatozoan catastrophes. Numerous contraceptive targets abound and several of these targets are worthy of further exploratory work, including blocking transmembrane ion currents (Kirichok et al., 2006; Brenton et al., 1996), disrupting Sertoli-germ cell adhesions (Cheng et al., 2002, 2005) and disruption of spermiogenesis by imino sugars (Walden et al., 2006).
Immunocontraception, which showed great promise for many years, has lost its appeal. Nevertheless, immunocontraception can be used as a strategy to discern the function of target molecules in the male. As an example, EPPIN is an epididymal protease inhibitor that coats the surface of human spermatozoa. EPPIN modulates PSA (prostate specific antigen, a serine protease) activity and the hydrolysis of semenogelin. Although EPPIN modulates the hydrolysis of semenogelin by PSA, antibodies to EPPIN do not inhibit PSA activity.
Ejaculate spermatozoa of monkeys and humans are coated with EPPIN. On the surface of spermatozoa EPPIN binds the protein semenogelin, which is secreted by the seminal vesicles during ejaculation. The EPPIN-semenogelin complex is removed during liquefaction of semen during the first 30 minutes after ejaculation. Failure to remove semenogelin results in infertile spermatozoa. Studies of the interaction of EPPIN and semenogelin, and their effect on human spermatozoa, are described, for example, in Wang, Z., Widgren, E. E., Sivashanmugam, P., O'Rand, M. G., and Richardson, R. T. 2005. Association of EPPIN with semenogelin on human spermatozoa, Biology of Reproduction 72 (4): 1064-1070 (Dec. 8, 2004).
One strategy for developing new contraceptives is to immunize primates with specific sperm surface antigens and determine the effects of the immune response on the ejaculated spermatozoa of immunized males. Recent work on EPPIN, (SPINLW1; serine protease inhibitor-like, with Kunitz and WAP domains-1) provides an example of the utility of the immunocontraceptive approach (O'Rand et al., 2004; Wang et al., 2005; O'Rand et al., 2006). A fertility study (O'Rand et al., 2004) demonstrated that effective and reversible male immunocontraception in primates is an obtainable goal. A high serum titer (>1:1000) sustained over several months achieved an effective level of contraception. Treatment of human spermatozoa with antibodies to EPPIN derived from primates showed a decrease in motility of the treated spermatozoa, (results are described, for example, in O'Rand, M. G., Widgren, E. E., Beyler, S. and Richardson, R. T. 2009. Inhibition of human sperm motility by contraceptive anti-EPPIN antibodies from infertile male monkeys: effect on cyclic adenosine monophosphate, Biology of Reproduction 80: 279-285 (Oct. 22, 2008).
The data were obtained from the analysis of affinity purified anti-EPPIN antibodies. Compared to control, there was a significant difference in the progressive motility of human sperm after treatment with anti-EPPIN antibodies as judged by a decrease in the total distance traveled by 71% (p<6.26×10−10) and the straight line distance by 57% (p<5.37×10−25), while the velocity decreased by 71% (p<3.96×10−8). At the same time the antibodies had the effect of increasing the bend angle between the straight-line vector (distance) and a turn, i.e. the back and forth movement of the head (tortuosity).
Consequently, in addition to whatever conclusions one may wish to draw about the feasibility of using immunocontraception, one can conclude from these studies that EPPIN has an essential role in fertility.
Antibodies are prone to degradation in the stomach if orally administered, and for this reason, are commonly administered by injection. Because it is unlikely that male contraception will be viable if it requires routine injections, it would be advantageous to have small molecules that also bind EPPIN and inhibit anti-EPPIN or semenogelin binding. The present invention provides such compounds, an assay for identifying such compounds, and methods for their use.